1,3-propanediol (PDO) is a compound having multiple uses. It is used as a monomer unit in the production of polyesters and polyurethanes that are useful as films and as fibers for carpets and textiles. It is also useful as an engine coolant.
PDO may be prepared from ethylene oxide (EO) in a process involving two primary reactions. First, EO and synthesis gas (H2/CO) are catalytically hydroformylated to 3-hydroxypropionaldehyde (HPA) in an organic solvent. The HPA is extracted from the solvent with water to form an aqueous solution of HPA, and the aqueous solution of HPA is then hydrogenated to form PDO.
The hydrogenation of HPA to PDO is performed using a hydrogenation catalyst. The hydrogenation catalyst should desirably have several features: 1) it should be highly active over an extended period of time; 2) it should cause the hydrogenation to be highly selective to the formation of PDO, rather than other compounds; 3) it should have a long catalyst life; 4) it should not be discharged into the PDO product stream; and 5) it should be economically cost effective, preferably using inexpensive components and, if required, as few expensive components as possible.
According to Hatch et al., U.S. Pat. No. 2,434,110, especially preferred catalysts for hydrogenating HPA to PDO are Raney nickel and Adkin's copper-chromium oxide. Hatch et al. also disclose that other suitable catalysts for hydrogenating HPA to PDO include catalytically active compounds of metals such as Fe, Co, Cu, Pd, Zr, Ti, Th, V, Ta, Ag, Mo, and Al. Slurry catalysts such as Raney nickel are known to have high activity and selectivity in converting HPA to PDO as a result of the homogeneous distribution of the catalyst in the hydrogenation reaction mixture.
Suspended or slurry catalysts, such as Raney nickel, however, are susceptible to being discharged into the PDO product stream in the form of soluble compounds, necessitating additional steps to purify the PDO product stream. Haas et al., U.S. Pat. No. 6,232,511, discloses that a supported ruthenium catalyst, wherein ruthenium is supported on an oxide phase, is useful in the hydrogenation of HPA to PDO, and avoids the problem of the metallic portion of the catalyst polluting the PDO product stream. Use of the supported ruthenium catalyst in a fixed-bed is preferred. Particularly preferred oxide phase supports are disclosed to be oxide phases that are resistant to acidic media such as titanium dioxide, silicon dioxide, aluminum silicate, zirconium dioxide, and zeolites. Aluminum oxide and magnesium oxide are disclosed as having lower acid resistance.
Supported, fixed-bed catalysts must have strong support materials in order to have a long catalyst life. Hydrogenation in a fixed trickle bed configuration is favored by small catalyst particle size. Reduction of the particle size, however, reduces the crush strength of the catalyst, which reduces the catalyst life. Catalysts having low crush strength collapse more readily over time and eventually plug the catalyst bed, at which point the catalyst must be changed.
Support materials having high crush strength are generally those that have less porosity, such as α-alumina. Supports that are less porous, however, have less surface to support the active catalyst metals, and, as a result, have less hydrogenation activity.
It is an object of the invention, therefore to provide a catalyst for the hydrogenation of HPA to PDO, wherein the catalyst is a supported catalyst that has relatively high crush strength, high activity over the life of the catalyst, long catalyst life, and that is economical and commercially attractive.
It is also an object of the present invention to provide a process for using such a catalyst to produce PDO from HPA in a hydrogenation reaction, where the reaction converts a high rate of HPA to PDO at a high degree of selectivity, and, where the process is continuous, the volume/time yield of PDO from HPA is high.